1. Field of the Invention
The present invention relates to an image processing apparatus capable of suppressing the change of hue of color image signals as image data transferred from external devices and also capable of increasing a sharpness of outlines or boundaries of the image data.
2. Description of the Related Art
FIG.1 is a block diagram showing a configuration of a conventional image processing apparatus disclosed in a patent document whose laid-open publication number is JP-A-58/198969, xe2x80x9cMethod of sharpness for imagexe2x80x9d. In FIG. 1, the reference character S0 designates a sharp signal and U0 denotes un-sharp signal. The reference number 141 designates a subtracter. The subtracter 141 inputs both the sharp signal S0 and un-sharp signal U0 to calculate a difference (S0xe2x88x92U0) between both signals S0 and U0. A multiplier 142 inputs the difference from the subtracter 141. The multiplier 142 multiplies the difference (S0xe2x88x92U0) by a constant value k. A multiplier 143 inputs the result of the multiplication of the multiplier 142.
Next, a divider 144 inputs an image signal I0 and an image signal Ii. In order to obtain a sharpness highlighting signal, the divider 144 performs a division of image signals I0 and Ii and outputs a divisional result I0/Ii. The multiplier 143 inputs the result I0/Ii from the divider 144 and performs a multiplication of the result k(S0xe2x88x92U0) and the result I0/Ii. An adder 145 inputs both the image signal Ii and the result k(S0xe2x88x92U0) (I0/Ii) and adds them and outputs the result Iixe2x80x2 of the addition. That is, the image signal Iixe2x80x2 obtained by the sharpness processing can be expressed by the following equation (1):                               I          i          xe2x80x2                =                              I            i                    +                                                    I                i                                            I                0                                      xc3x97            K            xc3x97                                          (                                                      S                    0                                    -                                      U                    0                                                  )                            .                                                          (        1        )            
FIG. 2 is a block diagram showing a configuration of a conventional another image processing apparatus disclosed in the patent document whose laid-open publication number is JP-A-61/273073, xe2x80x9cEdge highlighting processing apparatus for color gradation image informationxe2x80x9d. In FIG. 2, the reference number 151 designates a RGB/brightness conversion unit, 152 denotes a RGB/YMC conversion unit, 153 indicates a multiplexer, and 154 designates an outline highlighting unit.
Both the RGB/brightness conversion unit 151 and the RGB/YMC conversion unit 152 input digital signals R, G, and B. The RGB/brightness conversion unit 151 outputs a brightness I. This brightness I can be expressed by the following equation (2).
I=0.30xc3x97R+0.59xc3x97G+0.11xc3x97Bxe2x80x83xe2x80x83(2).
On the other hand, the RGB/YMC conversion unit 152 performs only a complementary operation because R and G, B and Y, M and C are in a complementary color relationship, respectively.
The multiplexer 153 inputs an output as a result from the RGB/YMC conversion unit 152. The multiplexer 153 selects and outputs only one of three kinds of information Y, M, and C supplied from the RGB/YMC conversion unit 152 through input terminals of the multiplexer 153 according to a state of selection terminals. The outline highlighting unit 154 inputs the selected one, namely the YMC signal, from the multiplexer 153 through an input terminal of the outline highlighting unit 154. The outline highlighting unit 154 further inputs the brightness I from the RGB/brightness conversion unit 151. The brightness signal I is delayed per pixel according to a clock signal and then converted to intermediate data D1 that will be expressed by the following equation (3).
D1=2Inxe2x88x92(In+1+Inxe2x88x921)xe2x80x83xe2x80x83(3)
where In is a brightness I of the n-th pixel.
The intermediate data designate a result of an edge extraction operation. For example, the intermediate data D1 becomes 0 when the brightness I is not changed, and becomes a negative value or a positive value when the brightness I is changed.
Next, the intermediate data D1 are converted into a complementary coefficient D2 with reference to a table showing a relationship between edge extraction results and complementary coefficients. In the table showing the relationship between the edge extraction results and the complementary coefficients, the value 1 is set when the edge extraction result is 0, and the value is in 0 and 1 when the edge extraction result is a negative value, and the value is not less than 1 when the edge extraction result is a positive value. The final result can be expressed by the following equation (4) when the complementary coefficients D2 is multiplied by selected YMC signal.                     O        =                  {                                                                                          Y                    xc3x97                    D2                                                                                                                    M                    xc3x97                    D2                                                                                                                    C                    xc3x97                    D2                                                                        .                                              (        4        )            
FIG. 3 is a diagram showing the operation flow of an image processing method executed by another conventional image processing apparatus disclosed in the patent document whose laid-open publication number is JP-A-3/175876, xe2x80x9cEdge processing method for color imagesxe2x80x9d. In the conventional image processing method shown in FIG. 3, the color information obtained by scanning color documents by an image device are divided or resolved into a red component, a green component, and a blue component. Each of the red, blue, and green components is scanned per pixel and sampled. Finally, the sampled image information are used as input image data (R1, G1, B1).
The input image data R1, G1, and B1 are converted to three stimulus values X1, Y1, and Z1 for a target pixel and adjacent pixels that are adjacent to the target pixel in a specific pixel area (Step ST161).
Then, a CIE color coordinate x1 and y1 and a visual reflection factor Y1 are obtained based on the three stimulus values X1, Y1, and Z1 (Step ST162). A sharpness processing for the visual reflection factor Y1 is performed (Step ST163) by using the Laplacian filter, that is well known, in order to obtain the three stimulus values X2, Y2, and Z2 based on the CIE color coordinate x1 and y1 and the visual reflection factor Y2. Then, the three stimulus values X2, Y2, and Z2 are calculated by using the CIE color coordinate x1 and y1 and the visual reflection factor Y2 that has been obtained by the edge processing (Step ST164).
Finally, the three stimulus values X, Y2, and Z2 are converted to the image information R2, G2, and B2 (Step ST165) and those image information R2, G2, and B2 are then outputted as output image data to external image devices (not shown).
A concrete example for the above image processing will be explained.
In Step ST161, the input image information R1, G1, and B1 are converted based on the following equation (5).                               (                                                    X1                                                                    Y1                                                                    Z1                                              )                =                              (                                                            0.6067                                                  0.1736                                                  0.2001                                                                              0.2988                                                  0.5868                                                  0.1144                                                                              0.0                                                  0.0661                                                  1.1150                                                      )                    ⁢                                    (                                                                    R1                                                                                        G1                                                                                        B1                                                              )                        .                                              (        5        )            
At Step ST162, the CIE color coordinate x1, y1 and the visual reflection factor Y1 are calculated based on the following equations (6) and (7), respectively.                               x1          =                      X1                          X1              +              Y1              +              Z1                                      ⁢                  
                ⁢                              y1            =                          Y1                              X1                +                Y1                +                Z1                                              ,                                    (        6        )            xe2x80x83Visibility=Y1xe2x80x83xe2x80x83(7)
In Step ST163, the sharpness processing is performed by using the Laplacian filter. In this sharpness processing, when the visibility of a target pixel is Y1, and when the visibilities of adjacent pixels that are located at front, behind, right, and left pixels adjacent to the target pixel are Yb, Yc, Yd, and Ye, respectively, the degree xe2x80x9cParmxe2x80x9d of the sharpness can be expressed by the following equation (8).
Y2=Y1xe2x88x92Parmxc3x97(Yb+Yc+Yd+Yexe2x88x92(4xc3x97Y1))xe2x80x83xe2x80x83(8).
In Step ST164, the three stimulus values X2, Y2, and Z2 are calculated by using the CIE color coordinate x1 and y1 and the visual reflection factor Y2 that has been obtained by the edge processing. These three stimulus values X2, Y2, and Z2 are obtained by performing the inverse conversion function shown in the equation (6).
In Step ST165, the three stimulus values X2, Y2, and Z2 are converted to the image information R2, G2, and B2 by using the inverse function shown in the equation (5).
Because the conventional image processing apparatuses have the configurations and the functions described above, for example, the image processing apparatus as the conventional example 1 has a drawback that the sharpness of image is increased when the signal Ii is changed, but any sharpness of image is not changed or increased when the sharpness of image is not changed when the signal Ii is not changed and the change of color is changed. In addition, the conventional image processing apparatus requires to divide signals into a sharp signal and un-sharp signal. This causes to increase the processing time period. As a result, the total time period to perform image processing becomes long.
In addition, because the calculation for the brightness I is executed based on the equation (2) described above in the conventional image processing apparatus as the conventional example 2, there is a drawback that it is difficult to realize the function on a hardware.
Furthermore, because the three stimulus values are calculated based on the equation (5) described above in the color image edge processing method executed by the conventional image processing apparatus as the conventional example 3, there is a drawback that it is also difficult to realize the function on a hardware.
Accordingly, an object of the present invention is, with due consideration to the drawbacks of the conventional technique, to provide an image processing apparatus, that may easily been made on a hardware, capable of judging a change of input image signals between a target pixel and peripheral pixels adjacent to the target pixel based on a difference of signal strengths of them and also capable of highlighting a ratio of the change of input image signals with suppressing the change of hue of the input image signals.
In accordance with a preferred embodiment of the present invention, an image processing apparatus has judgement means and conversion means. The judgement means inputs input image signals of n color components (n is a positive integer not less than three) forming colors of a plurality of image pixels transferred from an external device in time series, calculates a synthesis signal value of a target image pixel per input color component in said input image signals by performing a division of a sum of signal strength values of said input image signal about said target image pixel by a value of the n-th power of 2, and calculates a synthesis signal value of reference image pixels per color component in said input image signals by performing a division of a sum of signal strength values of said input image signals about said reference image pixels adjacent to said target image pixel by using the value of the n-th power of 2, calculates a ratio of said synthesis signal values of each reference image pixel and said target image pixel per reference image pixel, and calculates a conversion parameter indicating a change rate of signal strength values of said input image signals per color component based on a total sum of said ratios of said synthesis signal values. The conversion means converts said input image signals to output image signals without a change of a ratio of signal strength values between said input image signals per n-color component based on said conversion parameter per color component obtained by said judgement means. Accordingly, this configuration and function of the image processing apparatus achieves to suppress any change of hue of the input image signals and to highlight a part of change of color of the input image signals, and to form the image processing apparatus on a hardware easily.
In the image processing apparatus as another preferred embodiment according to the present invention, said judgement means selects input image signals as one color component in said input image signals forming said n color components, calculates a sum of signal strength values of said input image signals about said target image pixel as said synthesis signal value of said target image pixel per selected input image signals, calculates a sum of signal strength values of said input image signals about said reference image pixels as said synthesis signal value of said reference image pixels per selected input image signals, then calculates said ratio of said synthesis signal values of said target image pixel and said reference image pixel per reference image pixel, and calculates said conversion parameter indicating the change of the signal strength value of said input image signals of said selected color component based on said total sum of said synthesis signal values. Further, in the image processing apparatus above, said conversion means converts said input image signals without a change of said ratio of said signal strength values between said input image signals based on said conversion parameter per color component obtained by said judgement means. Accordingly, this configuration and function of the image processing apparatus achieves to suppress any change of hue of the input image signals and to highlight a part of change of color of the input image signals, and to form the image processing apparatus on a hardware easily.
The image processing apparatus as another preferred embodiment according to the present invention, further comprises signal range calculation means for setting a signal strength value of said output image signal outputted from said conversion section as a new upper limit value when said signal strength value of said output image signal is over a predetermined value, and for re-calculating said signal strength value of said output image signal transferred from said conversion means without any change of said ratio of said signal strength values among said input image signals of said n color components (n is a positive integer not less than three), and for outputting re-calculated output image signals.
In accordance with another preferred embodiment of the present invention, an image processing apparatus has coordinate conversion means, judgement means, conversion means and reverse conversion means. The coordinate conversion means inputs input image signals of n color components (n is a positive integer not less than three) forming colors of a plurality of image pixels transferred from an external device in time series, converts said input image signals to brightness signals, chromaticness signals, and hue signals. The judgement means inputs said brightness signals, said chromaticness signals, and said hue signals transferred from said coordinate conversion means, calculates a ratio of a change of said input image signals among a target pixel and reference pixels adjacent to said target pixel by using a difference of vectors per brightness signal, chromaticnes signal, and hue signal, and calculates a total sum value of said differences of said vectors, and for calculating a conversion parameter per brightness signal, chromaticness signal, and hue signal by calculating an inner product of said total sum value and an unit vector of each of said brightness signals, said chromaticness signals, and said hue signals. The conversion means converts said brightness signals, said chromaticness signals, and said hue signals without a change of a ratio of signal strength values between said brightness signals, said chromaticness signals, and said hue signals based on said conversion parameters per brightness signal, chromaticnes signal, and hue signal. The reverse converting means converts said brightness signals, said chromaticness signals, and said hue signals outputted from said conversion means to output image signals of n color components forming colors. Accordingly, this configuration and function of the image processing apparatus achieves to suppress any change of hue of the input image signals and to highlight a part of change of color of the input image signals, and to form the image processing apparatus on a hardware easily.
In the image processing apparatus as another preferred embodiment according to the present invention, said judgement means calculates said conversion parameters indicating a change rate of the brightness signals by calculating a ratio of the brightness signals between said target pixel and said reference pixels per reference pixel and calculating the total sum of said ratios of said brightness signals, and wherein said conversion means converts said brightness signals, said chromaticness signals, and said hue signals without a change of said ratio of said signal strength values between said brightness signals based on said conversion parameters per brightness signal. Accordingly, this configuration and function of the image processing apparatus achieves to suppress any change of hue of the input image signals and to highlight a part of change of color of the input image signals, and to form the image processing apparatus on a hardware easily.
In the image processing apparatus as another preferred embodiment according to the present invention, the judgement means calculates said conversion parameters within a range of a lower limit value to an upper limit value for said conversion parameters.